1. Field of the Invention
The present invention relates to a passive Q-switch device for use with a laser system and more particularly to a solid state saturable absorber which can be scaled to handle high brightness laser sources in which the repetition rate, pulse width and energy is optically controlled.
2. Description of the Prior Art
Q-switches and saturable absorbers are generally known to be used with various types of laser systems. Such devices are known to be disposed within the laser cavity and are used to block the primary laser signal until a relatively high population inversion has occurred in the lasing medium of the power amplifier at which time the device allows oscillation within the laser cavity to generate a relatively short pulse width high average power laser pulse. Examples of such laser systems which utilizes Q-switches are disclosed in: "SINGLE MODE HIGH PEAK POWER PASSIVELY Q-SWITCHED DIODE PUMP Nd: YAG LASER by Afzal, et al., Optics Letters, vol. 22, No. 17, Sep. 1, 1997 pp. 1314-1316 "Cr Li SAF Thin Slab Zig-Zag Laser" by Mandl, et al. IEEE Journal of Quantum Electronics vol. 33 No. Oct. 10, 1997, pp. 1864-1868, and U.S. Pat. Nos. 4,191,931; 5,119,382; 5,408,480 all hereby incorporated by reference. Active Q-switches are known to be either electro-optically or acousto-optically switched in order to obtain relatively high peak power average power pulses. Electro-optical Q-switches are known to include a non-linear crystal, such as LiNbO.sub.3, BBO or KDP. In such electro-optically controlled Q-switches, a kilovolt level electrical pulse is directed to the non-linear crystal, which causes the crystal to become birefringent to create a high cavity loss in order to prevent oscillation of the primary laser signal until an optimal population inversion occurs in the lasing medium. Such electro-optical Q-switches require a relatively fast rising electrical pulse in the nanosecond range and can consume a relatively significant amount of electrical power.
Acousto-optical Q-switches are also known. Such acousto-optical Q-switches are known to utilize a crystalline material, such as quartz or TeO.sub.2. In such acousto-optical Q-switches, a high power radio frequency source is required to produce an RF acoustic wave which allows light to be diffracted out of the laser cavity.
In order to increase the reliability of lasers and eliminate the drawbacks of high power consumption and the need for a high frequency RF source, passive Q-switches have been developed. Such passive Q-switches are known as saturable absorbers. Various saturable absorbers are known which utilize a light absorbing material that saturates when the gain inside the cavity exceeds a certain level at which time the primary laser signal is allowed to oscillate within the laser cavity. Known saturable absorbers are known to have several drawbacks including amplitude fluctuation of the output pulses as well as lack of precise frequency control. Also, residual absorption leads to heating. Thus, there is a need for a controllable saturable absorber for use with laser systems.